APPARATUS FOR MACHINING TURBINE BLADES

Abstract: An apparatus (15) for and method of machining turbine blades (10, 11, 12, 13) utilising a machining apparatus having mounting means (16) for mounting the machine adjacent to the end of a turbine blade and having a machining head (31) automatically movable in three dimensions. The machine head (35) may carry a machine tool or a probe such as a Renishaw probe which can be used to sense the shape of the desired form to feed information into a computer so that the machine may be operated automatically to machine subsequent blades. The probe may also be used after machining to check that the machine part is in accordance with the desired form.

Description: Title: Apparatus for Machining Turbine Blades Description of invention The present invention relates to an apparatus for and a method of machining turbine blades and is primarily but not exclusively adapted for the machining of the ends of rotor blades and in particular tenons and similar formations which cooperate with means such as shrouds or cover bands that tie the blades to each other. The ends of turbine rotors are particularly prone to damage and erosion. Applicants have proposed new methods or repairing outer ends of turbine blades as disclosed in British patent specification nos. 2091 MOB, 2208483 and 2229657. In the latter of these patents it is proposed to remove an end part of the blade, replace the end part with a piece of new material that may be preformed but is deliberately oversize and then after heat treatment carry out a machining operation on the end part so that it conforms to the desired shape. It is also known to rebuild tendons that become broken, worn or eroded by laying on the material by welding in a succession of layers and then subsequently working the built up material to conform to the desired shape. It is the subsequent machining and working of the material that is not only extremely complicated but also time consuming and in particular because of difficult access when the blade is still in a turbine blade array attached to the rotor, much of the operation may have to be carried out by hand-held tool which, unless operated by a person with considerable skill, could leave the end of the blade in a less than perfect shape. It will be appreciated that in the use of the turbine there is a considerable force acting on a shroud to remove it from the ends of the blade and it is therefore absolutely essential that it is a precision fit on the tenon otherwise there will be inadequate strength in the connection between the shroud and the tenon which could lead to separation of the shroud from the ends of the blade. With, for example, a tenon it is absolutely critical that the tenon is correctly formed since any gap between the tenon and a hole in a shroud attached thereto could leave a gap which almost certainly lead to the premature failure of the connection between the shroud and the blade. It is an object of the present invention to provide a machine that facilitates the machining of the end of a turbine blade. According to the present invention, we provide a machine adapted to machine a formation on a turbine blade, said machine comprising: (a) a rotary machine head adapted to drive a cutting tool; (b) ' automatic movement means adapted to provide three dimensional movement of said machine head; (c) control means for controlling said machine head and said three dimensional movement means; (d) fixing means for fixing the machine relative to a turbine blade to be machined; (e) locating means for locating the machine on said fixing means, said locating means comprising a first adjustment means, enabling at least limited angular adjustment of the machine in a radial plane relative to the axis of the rotor on which a blade to be machined is secured, where the adjustment means enabling the machine to be fixed in a predetermined adjusted position in said radial plane Preferably said machine also comprises a second locating means further comprises a second adjustment means enabling at least limited angular movement of said machine in a plane normal to said radial plane and wherein said second adjustment means enables said machine to be fixed in a predetermined adjusted position in said plane normal to said radial plane. It is a second object of the present invention to provide a method of machining a formation on a turbine blade. According to another aspect of the present invention we provide a method of machining a formation on a turbine blade, said method comprising the steps of: (a) providing metal from which said formation is to be formed. (b) providing a machine adapted to machine said formation and having a machine head capable of carrying a machine bit or a probe (c) providing information to said machine to perform the required machining operation. (d) connecting a probe to said machine head and advancing said machine so that said probe contacts the said turbine blade in a predetermined position so that said machine is aligned with a predetermined datum position on said blade, (e) removing said probe and applying a cutting tool to said machine, (f) causing said machine to be operated in an automatic manner to machine said formation. Preferably, the blade being machined is held in a very secure manner to prevent undesired movement of the blade during the machining operation. Conveniently the blade may be clamped to a surface or object to which said machine is affixed. Alternatively, the blade to be machined may be clamped to other blades in the array and in particular at least an adjacent blade each side of the blade to be machined and the machine itself may be secured to the blade to be machined or the clamping means that is clamping the blade to be machined to adjacent blades. Preferably said machine is as aforedescribed. It is further envisaged that once the tenon has been machined, a probe such as a Renishaw probe made by Renishaw PLC may be inserted into the machine head and the shape of the end of the blade and/or tenon formation recorded and stored in any desirable form for future reference should, for example, a new turbine blade have to be made. The machine and its adjustment means is thus able to not only machine the blade in an accurate manner but also because of the adjustment means and automatic movement means lends itself highly suitable for carrying out a probe such as a Renishaw probe. Preferably, the machining operation and three dimensional movement of the machine head will be a computer controlled in a accordance with predetermined data which may have been obtained using a Renishaw probe which conveniently could be placed in the machine head and used to detect the shape and configuration of a tenon, obviously one that is in good condition and the information can then be stored and used to re-machine tenons and if necessary the end part of the blade following the insertion of a new piece of material or building up of the tenons by welding techniques. It is important that during the machining operation that the turbine blade being machined is held as firmly as possible since undesired relative movement between the cutting tool and the blade could lead to errors and/or a poor finished surface. One method of clamping the blade that has been found to be satisfactory is to form a partially enclosed box around the blade, which box is firmly clamped to a support surface, for example a support surface in which the machine may be mounted and then fill the box with a low point melting point metal, for example a tin/bismuth alloy. An alternative method of clamping the blade which is particularly applicable when several blades in array to which a new end part is to be machined is to mount the rotor or blade array so that it may be moved around its rotational axis so as to bring each blade to be machined in turn into position adjacent the machine, so that machining may be carried out. A work surface and movable clamp means such as plates adapted to contact the blade over a considerable surface thereof is provided securely mounted to the plates being ??the work surface and moved into engagement with the blade to be clamped and locked in such position. The blade may be machined when the blades are in such locked position and once the machining is completed, the blades may be moved out of register with the blade so that the array may be rotated to bring the next plate to be machined into register with the machine and once again, the blades moved to lock that blade into a firm position. Where it is not possible to provide a work surface, it is further envisaged the means for clamping the blades involve clamping means adapted to contact several blades in the array including the one to be machined, which clamping means could also involve the use of gauge plates locatable at least between the blade to be machined and the blade adjacent thereof to ensure that the blade to be machined is accurately located while the machining is carried out. Some embodiments of clamping means is disclosed in British Patent No. 2227191. The Renishaw probe can also be used to detect the end formation of a turbine blade and, given the information of the required dimensions of the tenons, if there is malformation of the end of the blade which may result in the tenon not being properly formed and perhaps leave a slight flat rather than an even curved surface, then minor adjustment to the position of the tenon could be made to ensure that such a flat does not occur. It is a very important feature of the method of forming a tenon of the present invention that the Renishaw probe can be used to detect the end formation of turbine blades so as to accurately locate the tenon so that it is aligned with other tenons and undue strain is not applied to any one of the blades when coverbands or shrouds are attached. Furthermore, it is equally important that each tenon can be properly formed so that it is not situated so close to the edge of the blade that a flat may be formed. If the tenon cannot be properly formed, the cover bands or shrouds are placed in position, then a small gap will exist and use may well lead to early failure of the tenon due to crevice corrosion and cracking. Alternatively, if it is evident that such a situation may occur and movement of the tenon is not possible, then remedial treatment could be carried out on the blade to ensure that the tenon may be properly re-machined. The machine of the present invention may be mounted on a work table to the type disclosed in British Patent No. 2233261. Alternatively, the machine could be mounted on the tool post of a rotor lathe or any other secure mount in proximity to the rotor so that access to the ends of the blades are possible. The first adjustment means are of great importance in ensuring that the machine head can be positioned at the end of the blade so that the cutting tool is normal to the end face of the turbine blade so that the tenons can be accurately cut. In some turbine blades the end face of the blades does not lie in a plane parallel to the rotor axis but is inclined thereto, hence the requirement in some instances for the second adjustment means. The machine is preferably computer controlled the machining of the end of the blade carried out in accordance with predetermined information. The information may be obtained by sensing the profile of another blade in the array which has not been damaged. Alternatively, where it is required to alter the end of the blade to improve efficiency for example, then information regarding the new profile may be presented to the machine in a manner to enable it to machine such a new profile. Where several blades in an array are concerned, the machine may be provided with a datum point which may be a reference position on the blade or "tool makers ball" to enable the machine to be reset prior to commencing machining of each blade. It is also envisaged that recordings may be made of the machining operation to be carried out, which recording may be visually displayed as a check that the correct machining operation has been carried out. It is further envisaged that after machining of the blade, after insertion of on inspecting probe into the machine, an accurate check of the machining operation may be carried out and information recorded and/or displayed so that if there is any deviation of the shape required, a further machining operation can be carried out on the blade. The invention will now be described in more detail by way of example only with reference to the accompanying drawings, wherein: FIGURE 1 is a diagrammatic view of a machine of the present invention; FIGURE 2 illustrates one form of clamping of a turbine blade; FIGURE 3 shows two tenons in profile; and FIGURE 4 illustrates the end of a blade where the end face of the blade lies in a plane obliquely angled to the rotor axis. Referring first to Figure 1, part of a turbine blade array is shown and in particular turbine blades 10, 11, 12 and 13 all of which may form part of an array of, for example fifty blades, extending from a rotor shaft. The complete rotor may be placed on a stand similar to that described in British patent No. 2233261 and a part of the work bench is shown at 14. A machine generally indicated at 15 is firmly secured to the work bench 14 and comprises a base member 16 which may be bolted or otherwise secured to the work bench 14, the base plate 16 having rotatably mounted thereon a support member 17 provided with a peripheral thread form 18 and which is engageable with an adjustment generally indicated at 19 having a manually engageable part 20 and a shank with thread form 21. Rotation of the manually engageable part 20 will have the effect of causing rotational movement of the support member 17 relative to the base member 16. Extending from the support member 17 are a pair of upstanding plates 22, 23 which carry two further plate members 24, 25 through journal 26. The plate 25 is provided with a peripheral thread form as shown at 27 which is engageable by a thread form 28 provided on adjustment member 29 provided with a manually engageable part 30. The adjustment member 29 is secured relative to the support member 17 and rotation thereof causes movement of the machine 15 in an angular direction normal to the angular movement provided by adjustment member 19. Secured to the plates 24 and 25 is a cutting machine having a machine head 31 and an automatic movement system providing three dimensional movement, drive system 32 providing movement in a generally vertical direction, drive system 33 providing movement in a generally horizontal direction and drive system 34 providing movement towards and away from the work piece. The drive systems 32 to 34 may be operated by any suitable power means, for example electric motors and may be controlled in accordance with predetermined information via a computer 36 so a to move the machine head 31 and hence a machine bit 35 which may for example comprise a milling cutter in a very precise manner to effect machining of tenons for example on the end of a turbine blade 10. The first adjustment means 19 and second adjustment means 29 ensures that the cutting tool 35 can be aligned so that the rotational axis of the cutting tool 35 is normal to the end face of the blade 10 thereby ensuring that the cutting tool can properly machine the surface of the tenons. The computer 36 is shown connected to a junction box 37 which has a flexible lead 38 providing connection to the drive systems 32, 33 and 34 that provide three dimensional movement of the machine head 31 and the flexible lead 38 may also take the drive power to the machine head 31 in the case where a machine head 31 is an electric motor. Also connected to the computer 36 which is an optional visual display unit 37 which may be used to display information indicating for example, the desired forms to be machined and possibly a variation between the machine form and the required form, or any other useful information. Referring now to Figure 2, it is essential that the blade milling machine is held in as secure a manner as possible. One form of securement shown diagrammatically in Figure 2 comprises a pair of stands 40 and 41 having respective feet 42, 43 and 44, 45 which are secured in a removable manner to the work bench 14. The stands 40 and 41 support a box-like member generally indicated at 46 which, apart from an open top, surrounds the turbine blade 10 and into which a low temperature melting alloy is poured to partially encase a part of the turbine blade 10 and once the metal alloy has set the blade is held very firmly, the box-like member 46 including the low melting point alloy 47 being secured to the stands 40 and 41 via lugs 48 and 49 and securing members 50 and 51. It is envisaged that further or alternative clamping mens may be used to clamp the blade, for example a further work bench 40 may be moved into position adjacent the blade 10 and sliding clamping members be engaged with the further work bench and come into contact with various parts of the blade 10 so as to securely clamp the blade to the further work bench. It is also envisaged that the blades may be clamped by having clamping members, some of which may be similar to those disclosed in British patent specification No. 2227191 which blades are clamped to each other thus making any single one of the clamped blades relatively immovable. Figure 3 is an illustrated of the end of a blade, for example the blade 10, showing a single profile of a pair of tenons 52 and 53 and Figure 4 illustrates an alternative turbine blade 55 in which the end face 56 lies in a plane that is not coaxial with the axis of rotation of the rotor hence requiring movement of the second adjustment means so that the cutting tool can be brought into proximity with the end face 56 to machine the tenon shown at 57 with the rotational axis of the cutting tool 56 being normal to the plane in which the face 56 lies. It will be appreciated that the diagrammatic illustrations of the machine shown in the drawings is merely an example and the machine and adjustment means may take any suitable form as may the means for clamping and holding in a very secure position the blade to be machined. The features disclosed in the foregoing description, or the accompanying drawings, expressed in their specific forms or in terms of a means for performing the desired function, or a method or process for attaining the disclosed result, may, separately or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

Claims: CLAIMS 1. A machine adapted to machine a formation on a turbine blade, said machine comprising: (a) a rotary machine head adapted to drive a cutting tool, (b) automatic movement means adapted to provide a three dimensional movement of said machine head, (c) control means for controlling said machine head and said three dimensional movement means (d) fixing means for fixing the machine relative to the turbine blade to be machined (e) locating means for locating the machine on said fixing means, said locating means comprising a first adjustment means, enabling at least limited angular adjustment of the machine in a radial plane relative to the axis of the rotor on which a blade to be machined is secured, where the adjustment means enabling the machine to be fixed in a predetermined adjusted position in said radial plane. 2. A machine as claimed in Claim 1 wherein said locating means further comprises a second adjustment means enabling at least limited angular movement of said machine in a plane normal to said radial plane and wherein said second adjustment means enables said machine to be fixed in a predetermined adjusted position in said plane normal to said radial plane. 3. A method of machining a formation on a turbine blade, said method comprising the steps of: (a) providing metal from which said formation is to be formed. (b) providing a machine adapted to machine said formation and having a machine head capable of carrying a machine bit or a probe (c) providing information to said machine to perform the required machining operation. (d) connecting a probe to said machine head and advancing said machine so that said probe contacts the said turbine blade in a predetermined position so that said machine is aligned with a predetermined datum position on said blade, (e) removing said probe and applying a cutting tool to said machine, (f) causing said machine to be operated in an automatic manner to machine said formation. 4. A method as claimed in Claim 3 wherein said probe is adapted to sense the outline of the part of the blade to be machined prior to said machining operation to ensure that there is sufficient metal for the desired formation to be formed. 5. A method as claimed in Claim 3 or Claim 4 wherein the formation to be formed on the turbine blade is a tenon. 6. A method as claimed in any one of Claims 3 to 5 wherein after said formation has been machined, a probe is reinstated into the machine head and the shape of the machine formation is recorded and stored. 7. A method as claimed in any one of Claims 2 to 6 wherein the turbine blade being machined is secured by clamping means during said machining operation. 8. A method as claimed in Claim 7 wherein said clamping means comprises encasing at least part of said turbine blade in a solidified low melting point alloy. 9. A method as claimed in Claim 7 in said clamping means comprise movable engagement plates located in a work surface adjacent to the blade to be machined and movable into and out of contact with said blade. 10. A method as claimed in claimed in Claim 7 wherein said clamping means comprises clamping means adapted to clamp said blade relative to adjacent blades. 11. A machine substantially as hereinbefore described with reference to and as illustrated in Figure 1 of the accompanying drawings. 12. A method of repairing turbine blades substantially as hereinbefore described with reference to and as shown in the accompanying drawings. 13. A machine including any novel feature or novel combination of features as disclosed herein and/or illustrated in the accompanying drawings. 14. A method of machining a turbine blade including any novel feature or novel combination of features as disclosed herein and/or illustrated in the accompanying drawings.

Inventors: FRASER MICHAEL JAMES, FRASER, MICHAEL, JAMES
Applicants: FRASER MICHAEL JAMES, TURBINE BLADING LTD, FRASER, MICHAEL, JAMES, TURBINE BLADING LIMITED
Application year: 1994
Main classification: B23P6
IPC codes: B23C3, B23P6, B23Q1, F01D5